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Finding the Epidural Space – Neuraxial Blocks

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There has been a lot of progress in the department of anaesthetics since doctors performed the first etherisations in the 19th century. In the following article, you will gain an overview of the popular anaesthetic procedures, their indications and side effects – just as important in the clinical context as for the examination.

00:00
to do that way. How do we find the epidural
space? I pointed out to youpreviously that the epidural space is really
almost an imaginary space. It exists butit's not like a hole or an open area
in the body, it's an area that's packed fullof blood vessels and fat. But the interesting thing is,
that its major connection with the rest of the body is throughthe, through the thorax, through the chest.
And because of that, it changes pressurein the same way as the pressure in the chest
changes. And the pressure in the epiduralspace is lower than the pressure
in surrounding tissues. So, we can inserta needle, usually when we put it in we can feel the
Ligamentum flavum. It's usually a fairlytough ligament, except in pregnant women where it can be
quite soft. But it's usually tougher than the surrounding tissues.
00:51
And you can almost feel the tip of the needle popping
through it. And while we're advancing at, we're puttingpressure on the syringe, which is full of saline,
and as you pop through the Ligamentum flavum,you get what's called a Loss-of-Resistance, the syringe
just empties. And it's very sudden and verydramatic. People use different solutions
in the syringe. They use saline or air, ora mixture of the two. I used to use air, than I went
to a mixture of the two, I now always use saline.
01:21
And I get a very distinct feeling as you go through
the Ligamentum flavum and you losethe resistance that you're feeling as you
advance the needle. You then disconnectthe syringe from the needle hub and you pass
a catheter through the syringe, through the, excuseme, through the needle, which then passes
up into the epidural space. This is a typicalepidural needle, this is called a Tuohy needle.
And you can see it in the middle diagramhere. The Tuohy tip is quite
large. It's at a bit of an angleand if you look very carefully, you can see that
it's got a cutting edge. It's quite a sharp needle.
02:03
It'll actually cut through that Ligamentum flavum. On
the right part of the diagram you can see the catheterbeside the needle. Once the needle's in place
and you've done your loss-of-resistance, you takea stylet out of the needle and then you pass the catheter
through. So, what's the difference betweenan epidural and a spinal. Well, the big difference
is 3 millimeters and it's a very smalldistance when you're putting pressure on the back,
and you can feel the needle movingforward. But epidurals produce
good anesthesia, but notprofound anesthesia. So, patients with
an epidural block will feel pressurewhen the surgeon pushes
on their abdomen, may feel positionchanges as the surgeon moves back
and forth, and may have somesense of work going on. Sometimes
patients will actually describe thatthey can feel the surgeon's
hand, but they don't have pain.
03:09
It's a very good technique for patients in labor, because
you can use it for an extended period of time, becausea catheter is placed and you can give very dilute
local anesthetics over a period of time that causeexcellent labor pain relief. And then, if you have to,
you can change it to an anesthetic for surgicalpain. You could adjust the rate of flow through
the catheter, you can adjust the doseand strength of the local anesthetic
that's being used to modifyyour block to the patient's needs. But
the big difference between epiduraland sub-arachnoid block, as I said is 3 millimeters.
But the difference in block is quiteprofound. The first thing is that, when you
get into the spinal space, the sub-arachnoidspace, you're actually in the Central Nervous System. And you'll see
in a picture I'm going to show you in a moment, that youget cerebral spinal fluid dripping out of the needle.
You do not place a catheter in this situation.
04:09
You merely inject local anesthetic, sometimes
with very dilute morphine or othernarcotic into the space. You get
a very profound block. The patientshave absolutely no sensation below the waist
with this block. So, those sensationsof pressure or movement that I described for the epidural
are absent in the case of a spinal. Andfor the ideal surgical situation, a spinal
is actually superior to an epidural.
04:39
The negative about a spinal is, you can't adjust it.
You can't decrease or change the flowof the drug. It's a one shot technique.
So this is what happens with a spinal.

About the Lecture

The lecture Finding the Epidural Space – Neuraxial Blocks by Brian Warriner, MD is from the course Anesthesia.

Author of lecture Finding the Epidural Space – Neuraxial Blocks

Brian Warriner, MD

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